Modification of the Apex in Gastropod MoUusks. 689 



The sutures of the post-nuclear whorls are channeled. Color, in 

 all specimens examined, spermaceti-like. Two perfect specimens 

 examined. In this species the outline of the whorls forms a flat- 

 sided triangle from the periphery of the body whorl to the ex- 

 treme point of the apex. 



OliTella nivea Gmelin. (Fig. 12.) 



Apex large, knob-shaped, smooth, shining, consisting of two 

 and a-half rounded, rapidly increasing whorls. The first whorl is 

 large and very rapidly increases in size. A carina appears on the 

 last half of the second whorl and rapidly increases in strength. 

 The post-nuclear whorls are very deeply channeled at the suture. 

 Color porcelain white. A large number of specimens examined, 

 with little or no variation. The first one and a-half whorls vary 

 to a small extent in flatness. 



OliTella jaspidea Gmelin. 



The apex of this species is precisely like that of 0. venulata 

 Lam. See Fig. 9. 



Olivella miitica Say. (Fig. 13.) 



Apex small, knob-shaped, smooth, shining, consisting of two 

 and a-half carinated whorls, regularly enlarging ; the first whorl 

 enlarges more rapidl}^ than the second. The carina appears on the 

 second half of the first whorl, and is very strong ; the nuclear and 

 post-nuclear whorls are strongly channeled at the suture. Color 

 and texture like spermaceti. Five perfect specimens examined. 



Olivella nana Lamarck. (Fig. 14.) 



Apex small, flattened, smooth, shining, consisting of one and 

 a-half carinated whorls, rapidly enlarging ; the carina appears on 

 the first half of the first whorl and is very strong; the sutures of 

 both nuclear and post-nuclear whorls are deeply channeled. 

 Color dark, shining horn. This is the flattest apex in this genus. 

 A large number of specimens have been examined, and the only 

 variation appears to be in the extent of coloration, which changes 

 from horn to white in some specimens where the nuclear whorls 

 join the post-nuclear, and in others it is continued on the first or 

 second post-nuclear whorls. 



Olivella gracilis inconspicua Adams. 



The apex of this species is in all respects like nana in form (it 

 may be a little more rounded in some specimens) and diS'ers solely 

 in color, being pure spermaceti white. Two specimens examined. 



